The present invention relates generally to duct systems for the containment of electrical wiring, conduits, or other similar objects and, in particular, to an improved one-piece plastic duct system in which the duct channel cover is integrally formed and attached to the wiring channel by a flexible plastic hinge member. Importantly, the present duct system facilitates repeated access and closure of the duct channel without physical fatigue of the cover-to-channel hinge attachment member.
The present invention represents an improvement over applicant's earlier plastic duct system described in U.S. Pat. No. 4,602,124. This latter duct system, the disclosure of which is hereby incorporated by reference, describes a conventional two-piece duct arrangement whereby the cover forms a second detachable member that is removable from, but snaps over the first channel member to effect closure. Although not forming a part of this invention, it is contemplated that the present duct system may advantageously employ the same duct system interface and terminal components described in the above patent and therefore reference is made to that patent for those having interest in duct system interfaces and terminations.
Although one-piece duct systems are known, each of the known systems exhibits deficiencies that renders the respective structure unsuitable as a repeated access channel system. For example, in one system the channel and channel cover are integrally extruded. These members are interconnected by a thin hinge section--also forming part of the integral extrusion--and fabricated from the same relatively rigid plastic material forming the associated channel and cover. The hinge is made "thin" to secure the desired flexibility.
This system performs acceptably as long as repeated access to the duct channel is not required as, by way of example, when additional cables or cable rewiring is attempted. Although new wiring installations can often be planned and effected with a single duct access, it is not uncommon in such instances that changing circumstances dictate subsequent modification--i.e. the removal, addition, or rerouting of wires and cables--with its corresponding repeated flexure of the thin hinge material. Hinges extruded from the same material as that of the channel and cover are inherently brittle and fatigue after relatively few closure cycles. Any failure of the hinge, i.e. by the cracking separation thereof, quickly propagates along the entire longitudinal distance of the extrusion thereby rendering further use of the duct channel impossible.
The present system, by contrast, does not employ a thin hinge member fabricated of the same rigid plastic material defining the basic channel and cover. Rather, a co-extrusion process is employed whereby the channel, cover, and hinge are all simultaneously extruded as a single integral structure, but where dual-durometer materials are employed permitting a hinge of a more flexible, lower durometer plastic composition to be incorporated. Such material is inherently more flexible and is suitable for a large number of flexures. In this manner repeated access to the duct system may be achieved without the corresponding system failures common with single material extrusion designs.
The use of lower durometer hinge materials, however, has not heretofore met with complete success--such use generating its own unique set of deleterious effects resulting in a less than satisfactory duct system. These effects are attributable to the very flexure property of low such durometer material that renders it suitable as a hinge material in the first instance. Low durometer hinges have been observed to flex both in the transverse lateral and downward modes. Such flexure can result in improper latching of the duct cover and channel (i.e. maintenance of the "closed" condition of the duct system) as well as the compression of duct upon inadvertent duct contact, for example, through movement of furniture or striking by persons walking nearby. Such compression may cause visually observable distortions to the duct (i.e. aesthetically displeasing) as well as compromising or aggravating the above-noted latching problem.
The present one-piece duct arrangement adopts the advantages of multiple access afforded by dual-durometer extrusion but largely eliminates the associate difficulties through the use of a longitudinally extending cantilever tension arm or support member. This member is integrally extruded of the higher durometer plastic material defining the channel and cover and extends upwardly from the channel adjacent the hinge. This cantilever support member provides a lateral bias to the channel cover when such cover is in its closed orientation thereby overcoming the inherently weak hinge material to provide a corresponding locking bias between the cover and channel latching members. In this manner the channel cover is held in the latched condition with substantially the same force as would have been obtained from a high durometer, non-flexible hinge, but without the multiple flexure fatigue problems associated therewith.
Further, the support member may extend upwardly to a point immediately below the inner surface of the channel cover thereby serving as support against the downward compression of the cover upon inadvertent contact therewith. In this manner, the overall rectangular cross-sectional configuration of the duct system is maintained, in turn, precluding the above-noted aesthetic and structural latching problems associated with duct compression.
It is therefore an object of the present invention to provide a one-piece plastic duct system in which the user need not separately handle the duct channel cover and in which the channel cover integrally comprises an overall duct system including the duct channel itself.
It is a further object that the present one-piece duct system facilitate substantially unlimited access in which the cover may be opened and reclosed numerous times thereby permitting reconfiguration of the wiring and cables therein. And it is therefore an object that the a hinge arrangement be provided between the respective channel and cover members and, further, that such hinge be integrally formed with said members and not fatigue or otherwise break upon multiple opening and closing cycles of the duct system.
It is yet another object of the present one-piece duct system that the duct remain properly closed and latched and that the general cross-sectional contour and duct appearance remain substantially unchanged during normal usage.